Combined inhibition of MEK and BET downregulates surface expression of inhibitory immune checkpoint ligands and inhibits Nras^G12D/+;Asxl1^−/− AML cell growth in vitro. (A) Expression levels of H3K4me3, H3K4me1, H3K27ac, H3K27me3, and total H3 in bone marrow cells from age 6 to 8 weeks or age 28 to 30 weeks controls (C), Asxl1^−/−, Nras, and NA mice were analyzed using western blot. (B) NA-AML cells were cultured in triplicate in 96-well plates in the presence of DMSO or various concentrations of trametinib and/or GSK525762 for 7 days. Cell proliferation was quantified using the CellTiter-Glo assay. Combination Index was calculated using a CompuSyn algorithm. An index value <1 indicates synergism. (C) NA-AML cells were cultured in vitro and treated with DMSO or trametinib and GSK525762 (combined) for 5 days. Surface expression of PD-L1, PD-L2, CD155, CD86, and CD80 were analyzed in Lin^–c-Kit⁺ cells using flow cytometry. Data are presented as mean + SD. *P < .05; **P < .01; ***P < .001.